a. The equation of AD I get y= -3/2x+5/2, for BE I get y= -3/10x+1/2, and for CF I get y= -3/2x+5/2.
b. If you set each equation to equal each other, you'll find the point they intersect at. After finding where they intersect, you'll find that they intersect each other at the same point.
*Sorry for the vague explanation
Hope it helps!